This invention relates to a novel electronic timing apparatus for use where precision time measurements are required such as in photographic processes.
Among the basic steps included in conventional photographic processes are the exposure of photographic film to an image, development of the film into a photographic negative and the production of a photographic print from the negative. Each of these steps involves reactions which are dependent upon several variables such as temperature, time, light, etc. Photographic print papers are light sensitive i.e. they undergo a reaction and retain latent image information when struck by light or some other form of actinic radiation. The extent to which a change takes place is generally dependent upon the amount of light energy striking the surface of the light sensitive paper. The total quantity of light which strikes the surface of the print paper is a function of the intensity of the light source as well as the time of exposure of the light sensitive paper to the light source. Thus, print exposure time is a very critical variable.
During the production of a photographic print it is not uncommon to experience photographic negatives which will not render a print which is in technical and/or asthetic tonal balance across the entire print surface. It is the usual practice for those engaged in the photographic printing trades to utilize "burning", "dodging" and "masking" techniques to remedy this condition. The method commonly used involves exposing the photographic print paper for a preset period of time, usually seconds, which will render a basic print. This step might include the use of "dodging" and/or "masking" techniques to reduce or eliminate light energy from exposing certain areas of the print paper. Thereafter, if it is determined that certain areas of the print are underexposed, these areas are reexposed for a select period of time utilizing "burning", "dodging" and/or "masking" techniques. The use of such staged printing can involve a multitude of reexposures and it is desirable for the reexposure time durations to be accurate, repeatable percentages of the original exposure duration in order to produce a print that is in technical and/or aesthetic tonal balance.
The printing process itself involves setting up an enlarger with the negative from which a photographic print is to be made. This is done under conditions that vary from normal room light to safelight conditions (i.e. a light source having a wavelength to which the photographic print paper is not sensitive) and a period when the enlarger light source is manually energized to permit focusing of the photographic image in the plane of the photographic print paper. After the selection of the appropriate photographic print paper and the determination of other variables, a photographic print is made by exposing the paper to the image from the enlarger by energizing the enlarger light source for a predetermined amount of time during which time the "dodging" and/or "masking" techniques might be used as explained above. The photographic print paper is then processed chemically to develop an image and then visually inspected to determine if certain areas require more or less exposure. If this is the case, the above procedure is repeated with a new piece of photographic print paper and in addition to the original overall exposure (which might include modifications to the "dodging" and/or "masking" techniques used), selected areas of the photographic print that require more exposure are reexposed (utilizing "burning", "dodging", and/or "masking" techniques) for a length of time that is a percentage of the original exposure time duration (e.g. 25, 50, 75 or 100% of the time of the original exposure time duration). The photographic print is developed, reinspected and the above processes are continued until a satisfactory print is obtained. It is to be understood that reexposure time duration can be the percentages depicted above or multiples thereof (e.g. 125, 150, 175, 200%, etc.). Additionally, while the aforementioned descriptions and procedures involve the production of a photographic print utilizing light sensitive photographic paper, similar procedures are frequently followed utilizing any one of many other light sensitive materials used in other photographic and graphic arts applications.
Since the time periods used for the initial and subsequent exposures are very critical, it is essential that a precision timing device be used. Moreover, arriving at appropriate reexposure time durations can become mathmatically and physically cumbersome and time consuming. It is frequently difficult to reset a timing device for subsequent reexposures because the process takes place in virtual darkness and the operator performing the work is often times preoccupied with other matters associated with the printing process such as attending to filter, selecting negatives or appropriate print paper, etc. This problem becomes more complicated as the number of reexposure stages increases since in addition to the required resetting of the timing device for each subsequent reexposure, the operator must remember or record the time durations for each reexposure.
While many timing devices are available which activate a safelight and deactivate an enlarger light after a preset period of time has elapsed, they do not have the capability of being conveniently reset to time subsequent print exposure durations that are accurate, repeatable percentages of the preset period of time.